Dual surface ionic pump with axial anode support



Nov. 16, 1965 w. KNAUER 3,217,974

mm. summer: IONIC PUMP WITH AXIAL ANODE SUPPORT Filed Nov. 23, 1962 2Sheets-Sheet 1 Nov. 16, 1965 w. KNAUER 3,217,974

DUAL SURFACE IONIC PUMP WITH AXIAL ANODE SUPPORT Filed Nov. 23, 1962 2Sheets-Sheet 2 the anode cylinder.

United States Patent 3,217,974 DUAL SURFACE IONIC PUMP WITH AXIAL ANODESUPPORT Wolfgang Knauer, Malibu, Calif., assignor to Hughes AircraftCompany, Culver City, Calif, a corporation of Delaware Filed Nov. 23,1962, Ser. No. 239,430 8 Claims. (Cl. 230-69) This invention relates toelectrical vacuum pumps and more specifically to ionic vacuum pumps ofthe Penning discharge type.

Vacuum pumps of the Penning discharge type for creating high vacuums ofthe order of l0 torr are known and in general comprise a pair ofparallel disks composed of a reactive cathode material and an openendedhollow cylinder suitable for use as an anode. The cathode disks areslightly greater in diameter than the anode cylinder, and are placed atthe respective extremities of and normal to the anode cylinder. Theentire device is immersed in a magnetic field parallel to the axis ofthe anode, and enclosed in an envelope connected to the apparatus to beevacuated. When a high electric potential difference is applied betweenthe cathode and anode members a discharge strikes. Positive ions fromthis discharge continuously bombard the reactive cathode elements, andsputter off some of the reactive material thereon. The sputteredmaterial is deposited on other exposed surfaces within the envelope tobe evacuated, particularly surfaces of the anode element. These depositsact as a getter; i.e., they remove gas molecules from within theenvelope by adsorption. This adsorption is the primary pump action;however, some gases such as the noble gases and hydrogen are removed bydirect ion burial in the cathode elements.

Investigation of the discharge mode in such ion pumps has revealed thatthe active discharge area is confined to a thin plasma layer which linesthe inside surface of The present invention is based upon the discoverythat under proper conditions such a discharge may also be made to occuron the out-side surface of the anode. With simultaneous discharges onboth the in and outside surfaces of the anode, the total dischargecurrent, and, hence, also the bombardment rate and the pump speed isgreatly increased. Furthermore, the fact that the discharge is in theform of a thin plasma layer at the anode surface means that the anodecylinder need not be restricted to either round or rectangular crosssections as used in conventional pumps but may have any desirable shapewhich may produce a maximum pumping rate.

It is therefore an object of the invention to provide an improved ionpump.

Another object of the invention is to provide an ion pump of increasedpumping speed for a given physical size by establishing simultaneousdischarges on more than one surface of the anode member.

Another object of the invention is to provide an ion pump with anodeand/or cathode members whose geometric configurations optimize the rateof pumping and simplify the mechanical construction.

These and other objects and advantages of the invention are realized bythe providing of a connection and/ or support for an anode member whichdoes not disrupt the electron motion within the plasma layer. This isachieved according to invention by providing the anode with a supportrod and/ or connecting lead which extends axially along the direction ofthe major surfaces of the anode and is fastened to the anode at an edgerather than on a wall or major surf-ace. In this way, the discharge pathon the wall surfaces of the anode remains completely unobstructed. Theanode may also be pro- 3,217,974 Patented Nov. 16, 1965 vided withmeander-type cross-section in order to provide maximum anode surface toobtain maximum discharge current and pumping speed. Unlike anodestructures of the conventional multi-cellular pumps, the meander-typeanode of the invention can be manufactured from a single mold.

These and other features of the invention will be described in greaterdetail by reference to the drawings in which:

FIGURE 1 is a sectional view of an ion pump according to inventionwherein the anode support rod is oriented to extend parallel to themajor surfaces of the anode;

FIGURE 2 is an orthogonal View of a corrugated cathode configurationhaving ridges and valleys extending radially to the major surfaces ofthe anode;

FIGURE 3 is a sectional view of a corrugated cathode with ridges andvalleys extending parallel to the major surfaces of the anode; and

FIGURE 4 is an orthogonal view of a corrugated anode which providesmaximal surface area for the total volume occupied by a given anodeelement.

Referring now to FIGURE 1, a Penning discharge pump employing theinvention is shown wherein an anode cylinder 2 is mounted between twocathode plates 4 and 4, which may be circular. T heseanode and cathodemembers are disposed within an envelope 6 which is adapted to beconnected to apparatus to be evacuated by means of a connecting tube 8.Magnetic means 10 are provided outside and adjacent the envelope 6 forestablishing a magnetic field within the envelope parallel to the majorsurfaces of the anode cylinder 2. The anode cylinder 2, the envelope 6,and the connecting tube 8 may be of any desirable metal, for example,stainless steel. The cathode plates 4 and 4 may be of a reactivematerial such as tantalum, for example. Anyone of a number of suitablematerials may be employed for the cathode members such as molybdenum,titanium, tungsten, niobium, zirconium, barium, thorium, magnesiumcalcium and strontium. In practice it may be desirable to provide a filmof reactive material on a base metal, such as stainless steel.

In the embodiment of FIGURE 1 electrical connection is made to the anodecylinder 2 in such a manner as to not disrupt the electron motion of theplasma sheet formed adjacent the anode Walls during operation. This isachieved in this embodiment by extending the electrically conductive rod12 parallel along the direction of the major surfaces of the anodecylinder 2. The rod 12 extends to the outside of the envelope 6 througha hole in the cathode disk 4 and thence through a hole in the envelope6. The rod 12 may be used to support the anode cylinder if desired. Therod is electrically isolated from the envelope 6 by means of a glassmember or plug 14 which is hermetically sealed in the hole of theenvelope 6 and to the rod 12. The edge 16, constituting a minor surfaceof the anode cylinder 2, may be welded or otherwise secured to the endof the rod 12 so as to be in good electrical conducting relationshiptherewith and preferably supported thereby.

In operation the pump 1 is connected to the apparatus to be evacuated bymeans of the connecting tube 8. A high electric potential is imposedbetween the cathode members 4 and 4 and the anode 2. A suitablepotential for this purpose may be of the order of 3,000 volts. At thesame time a magnetic field of the order of 1-2 kilogauss may be imposedacross the pump in a direction parallel to the axis of the anodecylinder. A Penning discharge sheath will be established on both sides(inside and outside) of the anode member 6 to enhance the pumping speedas described heretofore.

In FIGURES 2 and 3 embodiments are shown wherein the inner surface ofthe envelope constitutes or provides a reactive cathode surface. Theanode cylinder 2 is disposed between end cathode members 4 and 4' andwithin a cylindrical type cathode portion 5 which may be integral withor otherwise connected to the end cathode members 4 and 4. This cathodeconfiguration is designed to effect maximum pumping speed by thedischarge action along the outer anode surface. In FIGURE 2 the cathodeportion 5 is corrugated with relatively sharp folds extending parallelwith the major surfaces of the anode cylinder 2. In FIGURE 3 the foldsextend toward the major surfaces of the anode. These corrugated cathodesurfaces may be employed to effect greater sputtering action (andtherefore greater pumping speed) by providing a high angle of incidenceof ions from the discharge along the outer anode surface. The anode maybe supported or connected to a source of potential by the arrangementsshown in FIG- URE '1 and described in connection therewith. Thecylindrical cathode portion may be provided with an outlet 22 forconnectionlo the apparatus to be evacuated so that the gas to be pumpedmay be introduced into the space between the anode and cathode members.

In the embodiments described thus far the anode has been shown as around cylinder. Since the anode current is proportional to the totalanode area, an increase in the anode area as by a meander-type surfacewill result in an increase of the discharge current and therefore thepump speed as well. The only requirements are that the anode surface beclosed or continuous and parallel to the magnetic field. In FIGURE 4 acorrugated type anode cylinder 2 is shown satisfying these requirementsfor use in the ion pump of FIGURES 1, 2, or 3. In order to permit thedischarge to develop properly on both inside and outside surfaces of theanode cylinder the surface should not come closer to each other thantwice the sheath width and the radii of curvature of the anode shouldnot be smaller than one sheath width.

There thus has been shown and described an improved ion pump in whichthe Penning type discharge may be established and maintained on bothsides of an anode member. In addition alternatives have been shown anddescribed which in combination with the dual surface dischargecapability of the anode permits an even greater pumping action.

What is claimed is:

1. An ionic pump comprising an envelope adapted to be connected toapparatus to be evacuated, means for establishing a magnetic fieldwithin said envelope, an anode member within said envelope and having atleast two major surfaces parallel to said magnetic field and an endportion constituting a minor surface, connection means for said anodemember secured to said end portion only and extending parallel to saidmagnetic field, and reactive cathode means diposed in said envelope atan angle with respect to said major surfaces.

2. An ionic pump comprising an envelope adapted to be connected toapparatus to be evacuated, means for establishing a magnetic fieldwithin said envelope, a cylindrical anode member having inner and outermajor surfaces and an end portion constituting a minor surface, saidmajor surfaces being parallel to said magnetic field, connection meansfor said anode member secured to said end portion only and extendingparallel to said magnetic field, and reactive cathode means disposed insaid envelope at an angle with respect to said major surfaces.

3. The invention according to claim 2 wherein said reaction cathodemeans is disposed adjacent and across said end portion.

4. An ionic pump comprising an envelope adapted to be connected toapparatus to be evacuated, means for establishing a magnetic fieldwithin said envelope, an open-ended cylindrical anode member havinginner and outer major surfaces parallel to said magnetic field, reactivecathode means disposed adjacent the ends of said cylindrical anodemember and at an angle with respect to said major surfaces, connectionmeans for said anode member secured only to an end portion thereof andextending parallel to said magnetic field through said reactive cathodemeans and electrically isolated therefrom.

5. An ionic pump comprising an envelope adapted to be connected toapparatus to be evacuated, means for establishing a magnetic fieldwithin said envelope, an anode member within said envelope and having aplurality of major surfaces parallel to said magnetic field and an endportion constituting a minor surface, connection means for said anodemember secured to said end portion only and extending parallel to saidmagnetic field, and reactive cathode means disposed in said envelope atan angle with respect to said major surfaces.

6. The invention according to claim 5 wherein said anode member containsa plurality of folds extending parallel to said magnetic field therebyproviding said plurality of major surfaces.

7. An ionic pump comprising a corrugated envelope adapted to beconnected to apparatus to be evacuated, the inner surface of saidenvelope constituting a reactive cathode member, means for establishinga magnetic field within said envelope, an anode member within saidenvelope having at least two major surfaces parallel to said magneticfield and an end portion, and connection means for said anode membersecured to said end portion only and extending parallel to said magneticfield.

8. The invention according to claim 7 wherein said anode member containsa plurality of folds extending parallel to said magnetic field therebyproviding said plurality of major surfaces.

References Cited by the Examiner UNITED STATES PATENTS 2,032,179 2/1936Lowry 313205 2,993,638 7/1961 Hall et al 23069 3,070,283 12/1962 Hall23069 3,112,863 12/1963 Brubaker et al. 23069 GEORGE N. WESTBY, PrimaryExaminer,

1. AN IONIC PUMP COMPRISING AN ENVELOPE ADAPTED TO BE CONNECTED TOAPPARATUS TO BE ELEVATED, MEANS FOR ESTABLISHING A MAGNETIC FIELD WITHINSAID ENVELOPE, AN ANODE MEMBER WITHIN SAID ENVELOPE AND HAVING AT LEASTTWO MAJOR SURFACES PARALLEL TO SAID MAGENTIC FIELD AND AN END PORTIONCONSTITUTING A MINOR SURFACE, CONNECTION MEANS FOR SAID ANODE MEMBERSECURED TO SAID END PORTION ONLY AND EXTENDING PARALLEL TO SAID MAGNETICFIELD, AND REACTIVE CATHODE MEANS DISPOSED IN SAID ENVELOPE AT AN ANGLEWITH RESPECT TO SAID MAJOR SURFACES.